1. Field of the Invention
The present invention relates generally to optical fiber devices and methods, and in particular to an improved stretcher fiber and module for use in a chirped pulse amplification system.
2. Background Art
Chirped pulse amplification (CPA) is a technique for amplifying an ultrashort laser pulse up to the petawatt (1015 watt) level. A laser generates an output comprising a series of ultrashort pulses of relatively low power. These pulses are then fed into a stretcher module having a dispersion that causes the pulses to stretch out. The stretched pulse output is then fed into a high-power amplifier. The stretched, amplified pulses are then fed into a compressor module having a dispersion opposite to that of the stretcher module to produce a recompressed amplified pulse output. By stretching the pulses prior to amplification, it is possible to reduce the peak power of the pulses, and to avoid undesirable nonlinearities.
Currently, stretcher modules are fabricated using free space diffraction gratings. However, for a number of reasons, it would be desirable to use an all-fiber-based solution. Although there have been efforts to create a fiber-based stretcher, these attempts have fallen short. In one case, 400 meters of standard low-cutoff single mode fiber was used as a stretcher. However, as a compressor typically has a positive RDS, and a standard low-cutoff single mode fiber typically has a negative RDS, no dispersion slope match is readily obtainable. To overcome this issue, a complicated balancing of the slope mismatch and nonlinearities in the amplifier fibers is required. In another case, a fiber with an RDS of 0.0053 nm−1 at 1050 nm was described. That fiber matches a grating compressor with a dispersion of β2=−1.6 ps2 (D=2.7 ps/nm) at 1050 nm, and is of limited utility.